Tokkai Hei 11-275826 published by the Japanese Patent Office in 1999 discloses a motor/generator which drives a plurality of rotors independently by applying a polyphase alternating current to stator coils. The invention disclosed in Tokkai Hei 11-275826 forms a part of the invention that has been filed at the USPTO as U.S. patent application Ser. No. 09/275,785 on Mar. 25, 1999 before the priority date of this invention and was granted as U.S. Pat. No. 6,049,152 after the priority date of this invention.
Tokkai Hei 6-311783 published by the Japanese Patent Office in 1994 discloses a motor/generator provided with two groups of coil units each comprising three coils connected by a star connection and supplied with a three-phase alternating current. A control circuit detects neutral electrical potential of each coil unit and therefore detects disconnections, short circuiting and earthing of coils based on the obtained electrical phase differences.